1. Field of the Invention
The present invention relates to photographic devices which allow modification and control of the contrast of a photographed image.
2. Description of Related Art
In taking photographs, a photographer encounters numerous lighting situations. While a great many of these situations may be desirable, there are undoubtably many situations in which the photographer may find it desirable, if not necessary, to modify the lighting effects. One of the methods used to modify the lighting effects is through the use of filters placed in front of the photographic objective so that any light passing through the objective to, for example, a photographic film, is influenced by the filter.
There are three main groups of filters: (a) color filters for balancing the light sensitivity of the film with tungsten light or daylight, or for adding color to the image; (b) contrast filters for changing the contrast of the scene being photographed and for adding softness thereto; and (c) effects filters for creating special effects, such as fog, star effects, rainbows, multiple images, etc.
These filters all have one thing in common, i.e., they all have unchanging optical densities, which means they cannot be adjusted to different optical densities when lighting conditions change.
In motion picture photography, there are often situations when, in one shot, the lighting conditions change dramatically. An example of these changing conditions occur when a photographer "pans" the camera from one area to another. If the first area is bathed in sunlight while the second area is in deep shadows, the photographer is faced with a high contrast situation followed immediately by a low contrast situation. If the photographer selects a particular low contrast filter to overcome the contrast in the sunlit area, he will then lose needed contrast in the shadow area.